Protozoa:

Introduction:
• PROTOZOA derived from Greek word
“PROTOS” and “ZOON” meaning “first
animal” are eukaryotic protists.
• Occur generally as single cell.
• They are distinguished from other
eukaryotic protists by their ability to
move at some stage of life cycle and by their lack of cell wall.
• Colonies of protozoa also occur.
• In a protozoan colony, the individual cells are joined by
cytoplasmic threads or are embedded in a common matrix.
• The study of these eukaryotic protists is called
“PROTOZOOLOGY”.
CHARACTERISTICS OF PROTOZOA:
• Both sexual and Asexual reproduction occur in protozoa, the
majority of protozoa is reproduced by Asexually.
• Rely on other organisms for some necessities
• Locomotion by Flagella, Pseudopodia or by Both.
• Vary in size and shape, some are visible while others require
high magnification.
OCCURRENCE:
• THEY are found in all moist habitats. They are common in the
sea, in soil and in fresh water
• Free living protozoa have been found in the polar regions and
at very high altitude.
• Parasitic protozoa may be found in association with most
animal groups.
• Parasitic protozoa can modify their morphology and
physiology to cope with a change in host.
ECOLOGY:
Protozoa may be divided into;
• Free-living protozoa
 • Symbiotic protozoa
Free-living protozoa:
• Are found in variety of habitats.
FACTORS OF DISTRIBUTION:
• Available nutrients
• Light
• Moisture
• Other physical and chemical conditions
• Temperature
Symbiotic Protozoa:
The association between protozoa and their hosts or other
organisms can differ in various ways:
• In COMMENSALISM, the host is neither injured nor benefited,
but the commensal is benefited.
• ENDOCOMMENSALISM; The association when protozoan is
inside the body. E.g. protozoa live in the lumen of alimentary
tract.
• ECTOCOMMENSALISM; is represented by protozoa which
attach themselves to host’s body
• Mutualism occurs between some protozoa and their hosts, e.g.
certain flagellates are present in the Gut of termites and digest
the woody material eaten by the termites to a glycogenous
substance.
CLASSIFICATION:
The protozoa are divided into TWO groups;
1) PHYTOFLAGELLATES
2) ZOOFLAGELLATES
• PLANT like forms are known as PHYTOFLAGELLATES, e.g.
Euglena.
• Animal like forms are known as ZOOFLAGELLATES, e.g.
Trypanosoma Brucei (causing sleeping sickness).
MORPHOLOGY:
• The size and shape of these organisms show considerable
variation.
• Great morphological diversity
• Some have Two nuclei
• Macronucleus (contain many copies of genome)
• Micronucleus
• Variety in number and kinds of mitochondria
• Some have contractile vacuoles
• All produce trophozoites; some produce cysts
INTRACELLULAR STRUCTURES:
I. CYTOPLASM
II. NUCLEUS
III. PLASMLEMMA AND OTHER CELL COVERINGS
CYTOPLASM:
• Homogenous, show colors (green, brown, blue, purple due to
pigment)
• Has submicroscopic protein fibrils (myonemes, microtubule)
• Arranged in parallel
• Divided in two portions: ectoplasm & endoplasm
a. Ectoplasm-more gel like and endoplasm is voluminous and
fluid
b. Cell organelles are present (endoplasmic-reticulum,
ribosomes, Golgi complex, mitochondria, food vacuole,
contractile vacuole, kinetosome etc.
NUCLEUS:
• Eukaryotic nucleus has chromosomes, the nucleolar
substance, the nuclear membrane, nucleoplasm
• One or many
• Some have two
a. Macronucleus-large in size, controls the metabolic activities
and regeneration processes
b. Micronucleus-small in size concerned with reproductive
activity
PLASMALEMMA AND OTHER CELL COVERINGS:
• The cytoplasm with its various structures is separated from
external environment by a cell unit membrane called plasma
lemma.
• The plasma lemma not only provides protection but also
controls exchange of substances.
• Many protozoa have compound coverings of membranes
modified for protection, support and movement. Such
combinations of membranes are referred as Pellicle (plasma
lemma itself)
Feeding Structures:
• Pseudopodia in amoeba
• Lenticular feeding tubes-in suctorians
• Mouth(cytosome) in ciliates
a. Simple round opening
b. A slit like-remains open all the time in some and some have slit
which can be opened and closed and always located
anteriorly.
• Oral groove an indentation in the pellicle, guides food toward
the cytosome and act as a concentrating device.
• Peristome-this an oral groove with membranelles
• Cytopharynx-it is a region through which the food must pass
and is enclosed in the food vacuole
CYSTS:
• Non motile form protected by a membrane
• Many protozoa form resistant cysts at the certain time of their
life cycle such as Desiccation resistant, low nutrient supply
resistant or temperature resistant.
• Cyst wall is secreted as a closely fitting extracellular coat or
structure.
• Cytoplasm is commonly attached to the cyst wall at one or
several points.
• It is reduced in size and dormant.
• Sexual reproduction of sporozoa is invariably results in the
cyst
LOCOMOTORY ORGANELLES IN PROTOZA:
Organelles for locomotion:
• FLAGELLA- long whip like structure
• CILIA- short flagella arranged in rows or tufts
• PSEUDOPODIA- temporary extensions and retractions of the
body wall
• UNDULATORY RIDGES- small snake like waves that form in the
cell membrane and move posteriorly
Locomotor organelles used to help identify the type of protozoa.
External structures of Cells:
LOCOMOTER APPENDAGES
• Flagella: Long, sheathed cylinder containing microtubules
• Covered by an extension of the cell membranes function in
motility
• Cilia: similar in overall structure to flagella, shorter and more
numerous, found only on a single group of protozoa and
certain animal cells, function in motility, feeding and filtering.
• PSEUDOPODIA- temporary cell extension, use for movement
and gathering food

Reproduction of protozoa:
• Protozoa multiply by the different methods of reproduction.
• Asexual reproduction
 • Sexual reproduction (in some protozoa)
• Many protozoa are able to carry out both sexual and asexual
processes
• Some parasitic forms may have an asexual phase in one host
and sexual phase in another host
Asexual Reproduction:
• It occurs by simple cell division.
• The daughter cells are of equal or unequal sizes respectively
Asexually they are reproduced by following processes
i. Binary fission
ii. Multiple fission
iii. Budding
Binary Fission:
• In asexual reproduction if 2 daughter cells are formed the
process is called “binary fission”. e.g. amoeba
• Pseudopodia are withdrawn before the nucleus divides
• After the division of nucleus organism elongates and
constricts in the center in order to form 2 daughter cells.
Binary fission in amoeba:
• In amoeba the division plane is longitudinal along the body axis
and the covering constricts into two halves.
• This is the binary fission in amoeba with soft covering.
• In amoeba with rigid coverings part of cytoplasm protrudes
from the aperture (opening in the covering) to secrete a new
covering over its surface.
• After the formation of
new covering nuclear
division proceed and
binary fission is
completed by
cytoplasmic division.
Binary fission in
flagellates:
 • In flagellates’ fission is longitudinal along the major body axis
(except dinoflagellates).
• Flagella themselves are incapable of division they must be
regenerated from basal bodies.
• Multiplication of basal bodies proceed cell division.
• In dinoflagellates division is at right angle to the cell axis.
• Transverse fission is characteristics for ciliates.
Multiple fission:
• In multiple fission parental cell divides to form many daughter
cells.
• Division is proceeding by the
formation of multiple nuclei with in
the mother cell.
• The cells then cleave rapidly to
form a corresponding number of
daughter cells.
• Multiple fission is not as wide
spread as binary fission.e.g.
foraminifera, radiolaria and the heliozoa
• The best example of multiple fission is found in sporozoa.
Budding:
• Budding is a process in which sessile protozoa produce
motile offspring.
• The mother cell remains sessile and release one or more
swarming of daughter cells.
• The swarmer differs from the parent cells in the possession of
special locomotor organelles.
TYPES OF BUDDING:
1. Exogenous
2. Endogenous
• Definite exogenous budding is seen in suctorian when a
portion or portions of an adult sessile suctorian bud from the
parent develop cilia and swim away.
• In Endogenous budding, also occur in suctorian species in
which the swarmer is formed inside the mother cell.
Sexual reproduction:
• In sexual reproduction the fusion of two gametes occurs in
group of protozoa.
• Conjugation is occurred in which temporary union of two
individuals for the purpose of exchanging nuclear material.
• After exchange of nuclei the conjugants separate and each of
them give rise its respective progeny by fission or budding.
Regeneration:
• The capacity to regenerate lost part is characteristics of all
protozoa.
• When a protozoan is cut in two nucleated portion regenerates
but the a-nucleated portion degenerated.
• In general nucleus is necessary for regeneration.
Protozoal diseases:
❖ Malaria
❖ Diarrhea
❖ Trichomoniasis
❖ Toxoplasmosis
❖ Amebiasis
Diarrhea:
• It is a disease characterized by loose bowls.
• Types of diarrhea
 • Non-inflammatory (watery diarrhea, no blood or mucus in
stool, no fever or systemic signs, dehydration may occur)
• Inflammatory (frequent lower vol. stool, bloody or mucoid often
with fever or systemic signs, dehydration rare)
Causes
• Giardia intestinalis (a flagellate protozoan)
• The causative agents inhibit intestine and feeds upon amino
acids and vitamin in the food.
Symptoms
• Epigastric pain
• Abdominal discomfort
• Loss of appetite
• Headache
• Vomiting
• Fever
Transmission
• It is transmitted by cyst which come out in stool
• The house flies contaminate food stuffs and water and cyst
may enter in the human body through fesses contaminated
food and water
• Children are more susceptible to this disease
Treatment
• Loperamide used for its treatment
• This decrease the no. of bowel movements and make the stool
less watery
• Oral rehydration therapy
• Avoid fatty foods, spicy foods
Malaria:
Malaria is characterized by periodic attacks of fever
Causes
• It is caused by plasmodium species.
• A spore forming protozoan.
 Symptoms
• High fever
• Sweating
• Headache
• Chills
• Fatigue
• Muscle pain
• Vomiting
• Nausea
• diarrhea
• It is transmitted by female anopheles’ mosquito
Treatment
• Quinine, clindamycin
• Mefloquine, chloroquine quinidine
Trichomoniasis:
• About 3% of women in the US population have trichomonas
vaginalis, a sexually transmitted parasitic infection
• It is mainly found in mouth of elderly person with bad teeth
Causes
• Tetraflagellate protozoa are parasitic in human body
• T.Intestinalis
• T.vaginalis
Symptoms
• Infertility
• Abortion at 2-4 months
Treatment
• Metronidazole (4 tablets in a single dose)
• Tinidazole (4 tablets in a single dose)
Amebiasis:
It is parasitic infection of intestine
Causes
Caused by antamoeba histolytica (infective cyst stage and a
pathogenic and motile trophozoite stage)
Symptoms
• Fever
• Tenderness
• Stomach pain (cramping)
• Loose stools
Treatment
• Metronidazole (flagyl)
• Tinidazole
• Chloroquine, emetine anddehydroemetine can be used
• All these drugs are beneficial for treatment of amebiasis.
Toxoplasmosis:
• Caused by toxoplasma gondii.
• Toxoplasmosis is a leading cause of death from foodborne
illness in the US.
• Transmission to human
• Inhalation of cat feces
• Ingestion of under cooked meat containing oocysts
Symptoms
• Fever
• Fatigue
• Headache
• Body ache
• Swollen lymph nodes
Treatment
• Sulfonamide
• Pyrimethamine (daraprim)
• These two drugs widely used to treat toxoplasmosis in
humans.